The invention relates generally to a system and method for heat recovery from a geothermal source of heat, and in particular to a system and method for thermo-chemical heat energy transformation for hot dry rock heat source recovery applications.
Most of the world's energy requirements are currently met by nuclear power plants and fossil-based power plants. In recent years, gas-fired combined cycle plants have become popular due to their relatively lower capital investment requirements, and their ability to reduce emissions. While these and other types of power plants (e.g., hydroelectric facilities) currently meet the world's energy needs, they are, however, a subject of a strenuous environmental debate. Carbon dioxide emissions from gas and fossil-based power plants are speculated to be sources of global warming. The rapid consumption of gas and fossil-fuel reserves has led to numerous questions about the long-term sustainability of such resources. It is therefore desirable to develop sources of energy that are environmentally friendly, are easily available and are relatively independent of geopolitical uncertainties.
Geothermal energy harnesses the natural heat of the earth. The geothermal energy can be found in several forms, for example in hydrothermal reservoirs of steam or hot water trapped in rock; in the heat of the shallow ground, called as “earth energy”; in hot dry rock (HDR) found usually between 2.5 km or more, beneath earth's surface and at even shallower depths in areas of geologic activity; in magma, molten or partially molten rock, that can reach temperatures of upto 1200 C; and in geo-pressurized brine that are found 3.0 to 6.0 kilometer (km) below the earth's surface. Geothermal energy has been used in power generation for many years, but typically at locations emanating hot fluids, typically water and steam. The much more abundant HDR locations and other geothermal locations which provide low grade heat have not been very successfully developed. As in most power generation facilities, whether wet or dry, heat from geothermal formations is used to produce steam, and the steam, in turn, is used to drive a steam turbine coupled to a generator operable to produce electricity.
Typically, heat is extracted from the geothermal source by pumping water under high pressure through a reservoir. The water is pumped into the reservoir through a supply well. Water or steam is removed from the reservoir through a return well. The water is heated by the geothermal source, for example HDR as it passes through the reservoir from the supply well to the return well. From the production well, the water is returned to the surface where its useful thermal energy may be extracted. The water may be re-circulated back to the reservoir to mine more heat.
Typically, the temperature of the carrier fluid (water in the above example) determines how the geothermal energy can be used the hotter the fluid, the grater the range of possible applications. For example, the temperature of heat energy from the HDR source is in the range of 150–250 C, depending upon the quality of steam extracted. However, such HDR layers typically exist only at deeper levels, typically at depths of 2.5 km or more. Consequently, investment costs tend to be much higher for HDR facilities. Such facilities could be made more cost-effective, if energy could be more efficiently extracted from the returned, heated water and steam. Such gains in efficiency could help to offset the initial investment in drilling and development of the HDR or any other geothermal energy production facility.
Accordingly, there is a need for a technique that enables recovery of energy from the geothermal source by aiding in offsetting drilling and the associated costs, and increasing efficiency of energy extraction.